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The mechanisms of the reaction of NCCO with molecular oxygen are investigated at the G3MP2//B3LYP/6-311G(d,p) levels for the first time. The calculation results show that two mechanisms are involved, namely, O attack on α atom mechanism and O attack on β atom mechanism, with six products yielded. The most feasible channel is the addition of O2 to β atom in NCCO radical leading to the energy-rich intermediate IM1, NCC(O)OO, which can isomerize to a four-center-structure IM3, and then undergoes C–C and O–C bond fission to form P1(NCO + CO2) finally. The barriers are 27.3 and 25.4 kcal/mol, respectively. For other channels involved in the two mechanisms, with less stable initial adducts and higher barrier, they are less conceivable dynamically and thermochemically. [ABSTRACT FROM AUTHOR]

Abstract  (Pt–NbPO x )/multi-walled carbon nanotubes (MWCNTs) with different NbPO x MWCNTs were prepared by a simple microwave irradiation method. The (Pt–NbPO x )/MWCNTs catalyst was characterized, and the kinetics toward oxygen reduction reaction (ORR) was determined, compared with that of Pt/MWCNTs catalyst. It was found that 10 wt% NbPO x was the best loading in terms of current density. The number of exchange electrons for the ORR was found to be close to four on both (Pt–NbPO x )/MWCNTs and Pt/MWCNTs. [ABSTRACT FROM AUTHOR]

The radical-molecule reaction mechanisms of CH2Br and CHBrCl with NO2 have been explored theoretically at the UB3LYP/6-311G(d, p) level. The single-point energies were calculated using UCCSD(T) and UQCISD(T) methods. The results show that the title reactions are more favorable on the singlet potential energy surface than on the triplet one. For the singlet potential energy surface of CH2Br + NO2 reaction, the association of CH2Br with NO2 is found to be a barrierless carbon-to-oxygen attack forming the adduct IM1 (H2BrCONO-trans), which can isomerize to IM2 (H2BrCNO2), and IM3 (H2BrCONO- cis), respectively. The most feasible pathway is the 1, 3-Br shift with C–Br and O–N bonds cleavage along with the N–Br bond formation of IM1 lead to the product P1 (CH2O + BrNO) which can further dissociate to give P4 (CH2O + Br + NO). The competitive pathway is the 1, 3-H-shift associated with O–N bond rupture of IM1 to form P2 (CHBrO + HNO). For the singlet potential energy surface of CHBrCl + NO2 reaction, there are three important reaction pathways, all of which may have comparable contribution to the reaction of CHBrCl with NO2. The theoretically obtained major products CH2O and CHClO for CH2Br + NO2 and CHBrCl + NO2 reactions, respectively, are in good agreement with the kinetic detection in experiment. [ABSTRACT FROM AUTHOR]

The mechanism for the CH2SH + O2 reaction was investigated by DFT and ab initio chemistry methods. The geometries of all possible stationary points were optimized at the B3LYP/6-311+G(d,p) level, and the single point energy was calculated at the CCSD(T)/cc-pVXZ( X = D and T), G3MP2 and BMC-CCSD levels. The results indicate that the oxidation of CH2SH by O2 to form HSCH2OO is a barrierless process. The most favorable channel is the rearrangement of the initial adduct HSCH2OO (IM1) to form another intermediate H2C(S)OOH (IM3) via a five-center transition state, and then the C–O bond fission in IM3 leads to a complex CH2S. . .HO2 (MC1), which finally gives out to the major product CH2S + HO2. Due to high barriers, other products including cis- and trans-HC(O)SH + HO could be negligible. The direct abstraction channel was also determined to yield CH2S + HO2, with the barrier height of 22.3, 18.1 and 15.0 kcal/mol at G3MP2, CCSD(T)/cc-pVTZ and BMC-CCSD levels, respectively, it is not competitive with the addition channel, in which all stationary points are lower than reactant energetically. The other channels to produce cis- and trans-CHSH + HO2 are also of no importance. [ABSTRACT FROM AUTHOR]

The mechanisms of CH2SH with NO2 reaction were investigated on the singlet and triplet potential energy surfaces (PES) at the BMC-CCSD//B3LYP/6-311 + G(d,p) level. The result shows that the title reaction is more favourable on the singlet PES thermodynamically, and it is less competitive on the triplet PES. On the singlet PES, the initial addition of CH2SH with NO2 leads to HSCH2NO2 (IM2) without any transition state, followed by a concerted step involving C–N fission and shift of H atom from S to O giving out CH2S + trans-HONO, which is the major products of the title reaction. With higher barrier height, the minor products are CH2S + HNO2, formed by a similar concerted step from the initial adduct HSCH2ONO (IM1). The direct abstraction route of H atom in SH group abstracted by O atom might be of some importance. It starts from the addition of the reactants to form a weak interaction molecular complex (MC3), subsequently, surmounts a low barrier height leading to another complex (MC2), which gives out CH2S + trans-HONO finally. Other direct hydrogen abstraction channels could be negligible with higher barrier heights and less stable products. [ABSTRACT FROM AUTHOR]